1. Field of the Invention
This invention relates to a control joint for use in casting concrete sections and more particularly relates to a control joint which has a base and an upstanding web which will lock into the concrete to prevent shifting once it is poured.
As is well known, concrete foundations, sidewalks and similar concrete products have traditionally utilized wooden form work. Wooden form work has a disadvantage in that it utilizes wood sections which must be cut to size and then assembled on site and later removed. In some instances it is necessary to soak the wooden forms with oil making them heavy. Removal of wooden forms can be difficult. Furthermore, once the forms have been used, they either must be cleaned or discarded as scrap. Accordingly, the use of conventional wooden form work is time consuming, expensive and is an inefficient use of resources.
As a result, the industry has turned to other types of joints and supports for forming barriers and supports when pouring concrete structures such as floors and pads. The following are representative of the prior art in this area.
U.S. Pat. No. 4,815,886 shows a self supporting expansion joint for use in the preparation of concrete products which comprises a single unit inverted T having a flat base adapted to rest on the ground and a vertical beam perpendicularly joined to the center of the base. The beam is thicker at the point of junction with the base and at the top of the beam. In a special embodiment, the center core of the beam is prepared from by co-extrusion with a material which is more expandable and compressible than the material used in the remaining portion of the construction.
U.S. Pat. No. 4,909,002 discloses a concrete screen rail having generally parallel spaced top and bottom edges, at least the upper one of which is provided with a finished surface. A plurality of recesses are provided in a web portion of the rail. In use, the recesses in the web are closed off by a thin layer of concrete. The screen rail may be in the form of a straight beam of I-section or alternatively a general L shaped cross section. The rails are designed to become an integral part of the entire slab and to provide improved edge finish to the completed floor.
U.S. Pat. No. 5,433,051 discloses a supporting element for use in casting concrete floors which includes a base member and a distinct top member supported by the base member. The top member has an elongated top sliding plane surface allowing a concrete leveling device to be moved along it. The base member is formed of side walls with openings. The base member may form a grove in the central top portion and the top member may be an elongated rail received within the grove. Foot portions connected to side walls may have leveling adjustments screws provided in them for adjusting position of the top sliding plane surface. A flexible barrier may be disposed longitudinally between the side walls. This system is commercially available and sold under the designation Combiform.
While the aforementioned systems provide certain advantages while casting concrete pads and floors and may overcome many of the significant disadvantages attendant to use of a wooden forms, there nevertheless exists a need for an improved control joint which is self supporting and will effectively lock into the concrete product.
It is a broad object of the present invention to provide a control joint which may be easily installed, leveled and will resist the tendency of the concrete to heave or vertically shift.
It is another object of the present invention to provide a control joint that facilitates screeding during finishing of the concrete product.
It is another object of the present invention to provide a control joint which may be continuously extruded and provided in sections that may easily be cut to length upon installation.